2-Amino-1,3,4-thiadiazole (ATDA) and related compounds have uricogenic, teratogenic and antitumor activity, effects reversed by nicotinamide. Evidence indicates that ATDA is metabolized to a fraudulent nucleotide, of unknown structure, that strongly inhibits IMP dehydrogenase. The pathway for formation of the nucleotide has not yet been elucidated but probably involves an aminothiadiazole-containing NAD ion analog formed by exchange with the nicotinamide moiety of this molecule. The proposed work is designed to elucidate the mechanism of action and metabolism of ATDA and its derivatives. We propose to prepare labeled and unlabeled ATDA and three of its derivatives and test them for exchange with the nicotinamide of NAD ion. The NAD ion analogs will be cleaved with nucleotide by pyrophosphatase to yield fraudulent nucleotides, which will be tested for inhibition of IMP dehydrogenase purified from L1210 cells. The structure of the ATDA-containing nucleotide present in L1210 cells will be determined, as will the structures of the major urinary metabolites of ATDA.